# pkg_chk -g # make initial list of installed packages
# pkg_chk -r # remove all packages that are not up to date and
packages that depend on them
# pkg_chk -a # install all missing packages (use binary packages,
this is the default
# pkg_chk -as # install all missing packages (build from source)

is that the packages are deleted at once and one has to wait a long
time ( according to the order of updates ) to get some packages
updated.

For example I run samba and once the samba package is removed by -r
the users have to wait a long time till it is updated :-(

I usually run the pkg_chk -as (or pbulk) in a chroot to create packages
and then install the packages in my real system.